The function of an air intake manifold for an internal combustion engine is to feed the desired amount of air to the engine combustion chamber. To maximize engine performance (torque and/or horsepower), an air intake manifold will need to be capable of delivering as much air as possible for a given size (volumetric efficiency). One conventional method consists of tuning the intake manifold based upon its acoustic characteristics. This tuning will allow the air volume to move as fast as possible at a particular engine RPM where it attains acoustic resonance at the excitation frequency caused by the pumping work of the pistons. This results in a volumetric efficiency of intake air that is more than 100% for the given engine RPM, while at other RPM ranges, the efficiency drops below 100%.
In particular, for light trucks, the engine torque at low engine RPMs is an important performance feature, with a torque curve that is flat over a wide RPM band being very desirable. However, due to the acoustic resonance of a conventional tuned air intake manifold, it is limited in the width of RPM band that can be enhanced by acoustic resonance. Two possible solutions that have been addressed recently are variable valve timing technology for intake and exhaust valves and variable intake manifold geometry where the length and/or cross-sectional area of the air passages in the manifold are varied to allow for maximum volumetric efficiency at differing engine RPMs.
For variable intake manifold designs, a typical variable intake manifold is employed with engines having two intake valves per cylinder and port throttling, which allows for the closing of one of the two intake valve ports. While this solution can work adequately for most vehicles, it can be expensive for vehicles such as light trucks, which typically have larger V-type engines with at least six cylinders and where, typically, the engines are currently configured with only one intake valve per cylinder.
In a V-type engine, a typical tuned air intake manifold design may have a common air entry point. The intake air separates into two streams, one through each secondary runner, for each bank of cylinders. The intake air for each bank then enters an intake plenum or chamber and is distributed into each of the primary runners before going into the intake ports of the cylinder heads.
In an attempt to improve on this, a variable geometry intake manifold (having more than one tuned frequency) maybe employed. It is one in which its runner lengths are switched between long and short. A longer runner length will decrease the resonant frequency of the intake manifold and increase the intake airflow speed, and consequently, the maximum volumetric efficiency of the air intake will happen at lower engine speed. This provides good engine torque at low engine speed for better stop-and-go driving conditions.
When the variable intake manifold switches its air intake passage to short runner lengths, which allows a larger overall air flow, the intake manifold's resonant frequency increases and so does the engine speed where the maximum volumetric efficiency occurs. This provides a good engine horsepower at higher engine speed for better high speed driving performance without resorting to a two intake valve per cylinder arrangement.
In order to accomplish this, a typical variable geometry intake manifold adjusts the length of the primary or secondary runner through some sort of valving. The air intake manifold is further complicated by the fact that the engine is a V-type rather than in-line.
However, a typical variable geometry air intake manifold cannot provide as much tuning as is desirable within the space available in the engine compartment. There is a need to maximize the ability to change the length of runners and the volume of the plenum through which the air flows in order to maximize the ability to vary the tuning frequency of the manifold, while still minimizing the packaging space taken up by the manifold assembly in the engine compartment of a vehicle, particularly for V-type engines.